The primary objective is to investigate the mechanisms underlying the flow-related inhibition of tissue factor (TF) activity in vascular smooth muscle cells (VSMCs) observed in our laboratory. The time course of TF expression under applied laminar flow, the role of local flow conditions (wall shear rate) and the effects of increasing wall shear stress on the regulation of TF expression will be examined. Cultured rat and human VSMCs will be exposed to wall shear rates and shear stresses representative of stenosed blood vessels. At selected times both TF activity and TF mRNA will be measured to assess whether inhibition occurs at the level of transcription or at the level of protein activity. Tissue factor activity will be quantified by the production of factor Xa in the presence of factor VIIa and calcium and message evaluated by Northern blots. We will test the effect of increasing wall shear stress while maintaining wall shear rate by perfusing the cells with a high viscosity fluid. The studies are designed to increase our understanding of the regulatory role of fluid dynamic parameters in tissue factor mediated thrombosis.